Compression-ignition engine

ABSTRACT

Compression ignition engine comprising a prechamber communicating with the cylinder through a transfer passageway whose smallest diameter is 0.6 D3/4, D being the cylinder bore diameter expressed in millimeters, a piston provided with a protrusion adapted to penetrate said transfer passageway so as to leave an annular clearance therebetween which is at most 0.05 D3/4, with D expressed in millimeters, when the piston is at the upper dead center, said protrusion being such as to leave a free passage for the gases between the protrusion and the lower edge of the transfer passageway , which passage , during the downward stroke of the piston becomes equal to the minimum section with which the transfer passageway opens into the precombustion chamber, when the crankshaft has rotated from the piston top dead center position through an angle expressed in degrees of crankshaft rotation corresponding to between one half the duration of injection at full load and the whole of said duration.

O United States Patent 1191 1111 3,738,332 Eyzat et al. June 12, 1973 [54] COMPRESSION-IGNITION ENGINE 1,524,894 2/1925 Thompson et al. 123/32 7,526 928 T 1 1 Ecomal'die Pecmclaude Stephan, 1,691,302 11/1928 Peterson.... 123/32 Boulogne; Jea -C a G ers 1,696,799 12/1928 Held 123/32 Suresnes, all of France 1,772,742 8/1930 Barrett 123/32 1,838,495 12 1931 ON '11 123 32 [73] Asslgnee: France's Des 1,867,683 7/1932 s er r 123/32 Carburants Et Lubrrhants, Ruell'Malmalson France Primary Examiner-Laurence M. Goodridge [22] Filed: Apr, 8, 1971 Attorney-Craig, Antonelli & Hill [21] Appl. No.: 132,381 [57] ABSTRACT Compression ignition engine comprising a prechamber g" Appllcatlon Priority Data communicating with the cylinder through a transfer Apr. 15,1970 France 7013719 passageway whose smallest diameter is 0.6 D, D

being the cylinder bore diameter expressed in millime- [52] US. Cl. 123/32 R, 123/32 B, 123/30 D ters, a piston provided with a protrusion adapted to [51] Int. Cl F02b 3/00 penetrate said transfer passageway so as to leave an an- [58] Field of Search 123/32 R, 32 B, 32 C, nular clearance therebetween which is at most 0.05 123/32 SP, 30 R, 30 D D, with D expressed in millimeters, when the piston is at the upper dead center, said protrusion being such [56] References Cited as to leave a free passage for the gases between the pro- UNITED STATES TE trusion and the lower edge of the transfer passageway 1,942,127 1/1934 Russell et al 123/32 Passage the "f" 1,977,752 10/1934 Baj 123/32 Plston equal mlmmum Seem" 2,012,036 3/1935 Mack [23/32 which the transfer passageway opens into the precom- 2,026,321 12/1935 Quick 123/32 bustion chamber, when the crankshaft has rotated from 2,442,082 5/1948 French 123/32 the piston top dead center position through an angle 3,386,422 6/1968 Eyzat 123/32 expressed in degrees of crankshaft rotation corre- 3; w g h sponding to between one half the duration of injection ygo s y 1,354,786 10/1920 Tartrais 123/32 at full load and the whole of sad duration 1,419,702 6/1922 Tartrais 123/32 4 Claims, 6 Drawing Figures PMENIEUJUN I 2 I913 manure INVENTORS PiERRE EYZAT, ANDRE ECOHARD,

CLAUDE STEPHANTQnA JEAN-CLAUDE GHERSI 7 00. ,GmnJL 1v AME ATTORNE Y5 COMPRESSION-IGNITION ENGINE This invention relates to a new improved compression-ignition engine producing a much higher specific power than the presently available Diesel engines, and whose exhaust gases contain less of polluting substances.

The improvement of the performances of the presently available compression-ignition engines is limited by the maximum pressures which the parts of the engine can withstand, particularly the wall of the combustion chamber.

It would be theoretically possible to noticeably increase the power of a Diesel engine, provided that there could be achieved in the cylinders, a combustion developed at a substantially constant pressure, close to the maximum pressure compatible with the mechanical strength of the cylinders.

With a working cycle wherein the combustion is performed at constant pressure having a thermal output close to that of a cycle wherein the combustion is performed at constant volume, it would thus be possible to provide engines having substantially the same specific consumption as the conventional Diesel engines but a much higher power.

Up to now it has not been possible to achieve, in the combustion chambers of known type of a compressionignition engine, a combustion performed at substantially constant pressure, due to the decreasing combustion velocity accompanying the combustion progress. This feature has lead to conception of complex solutions, which are accordingly expensive, in view of establishing a greater similarity with the operating conditions of an engine where the combustion would be performed at constant pressure.

One of the suggested solutions consists in performing the complete combustion in a chamber separate from the cylinder and of transferring to the latter, under a substantially constant pressure, the gases issued from the separate combustion chamber.

This solution implies that the three functions: compression, combustion and expansion, be performed by three separate elements. In addition, in such a solution, the system performing the expansion is in contact only with the hot gases and never with the cold gases, in contrast with the piston of a conventional engine. Thus, such a solution, which is of a complex conception and restraining as to the thermal resistance, results in a high cost.

It is an object of this invention to provide a combustion-ignition engine which does not suffer from the above-mentioned disadvantages and produces a much greater power than the compression-ignition engines of the previously known types operated at the same maximum pressure in the combustion chamber or, conversely which produces the same power as any Diesel engine presently available on the market, operated at a significantly lower maximum working pressure, thereby resulting in both cases in a much more economical construction.

More particularly an engine according to this invention can be operated so as to provide the same mean effective pressure (M.E.P.) close to 16 atmospheres, as a direct injection engine of conventional type, i.e., with the same cylinder bore diameter, to produce the same power as said engine, with a maximum pressure in the combustion chamber of only about 100 atmospheres instead of about atmospheres in the conventional engine, which considerably reduces the stresses to which are subjected the walls of the combustion chamber and therefore makes possible a lightening of the engine construction and a cost reduction.

Conversely when constructing an engine so that it can withstand a maximal pressure of 140 atmospheres in the combustion chamber, such as a direct injection engine of conventional type for which the mean effective pressure obtained is about 16 atmospheres, there can be obtained by the invention a mean effective pressure close to 26 atmospheres, thereby resulting in a power increase of about 60 percent.

Of course such an increase in the mean effective pressure implies the use of a turboblower adapted to sufficiently compress the air introduced in the combustion chamber (supercharged engine), but there is no increase of the maximum stresses to which are subjected the walls of the combustion chamber, since the maximum pressure is still 140 atmospheres.

These objects are achieved according to this invention by providing a compression-ignition engine having at least one cylinder, the bottom of which includes a prechamber in communication with the cylinder through a transfer passageway, the piston of the engine being provided with a protrusion adapted to penetrate the transfer passageway towards the end of the compression stroke, a fuel injector opening into the prechamber and directing the fuel jet towards the passageway, and wherein the combination of the following elements provides for a combustion at substantially constant pressure in the cylinder:

a. the transfer passageway opens into the prechamber through an opening whose smallest diameter, expressed in millimeters, is at most equal to 0.6 D D being the diameter expressed in millimeters, of the cylinder bore,

b. the annular clearance between the protrusion and the wall of the transfer passageway, when the piston reaches the top dead center position, is at most 0.05 D" D being also expressed in millimeters, and

c. the height of the protrusion is so determined that, during the downward stroke of the piston, the flow section left free for the flow of gases, between the protrusion and the lower edge of the transfer passageway becomes equal to the minimum section with which the transfer passageway opens into the precombustion chamber, when the crankshaft has rotated from the piston top dead center position through an angle expressed in degrees of crankshaft rotation corresponding to between one half the duration of injection at full load and the whole of said duration.

The invention is now illustrated more in detail with reference to the accompanying drawings wherein:

FIG. 1 is a partial cross-section of the upper part of an engine cylinder according to the invention,

FIG. 2 is an enlarged partial view of the engine of FIG. 1, showing the construction parameters involved,

FIGS. 2A, 2B and 2C are enlarged partial views similar to FIG. 2 and showing the positioning of the piston protrusion at various stages of engine operation,

FIG. 3 shows, by way of comparison, three curves representing the progress of the combustion respectively in a direct injection conventional engine, in an engine according to this invention and in an ideal engine wherein the combustion would be performed at constant pressure.

In FIG. 1, reference 1 indicates a cylinder of an engine, 2 a cylinder head, 3 and 4 respectively the inlet valve for the air used as combustion-sustaining agent and the exhaust valve.

In the cylinder head is arranged a prechamber 5 communicating with the cylinder through a transfer passageway 6 leaving free for the gases a passage whose section is defined by the bore section of an insert member 6a.

Piston 7 is provided at its upper part with a protrusion adapted to penetrate the transfer passageway towards the end of the compression stroke.

In the embodiment shown by way of example, the protrusion 8 has a substantially cylindrical shape but it would not be out of the scope of the invention to give to this protrusion a slightly frusto-conical shape widening out downwardly or upwardly, provided that the set of above-mentioned conditions which constitute the invention features i.e., the conditions relating to the transfer passageway, to the annular clearance between the same and the protrusion and the height of the latter, be fulfilled.

A fuel injector 9 opens into prechamber 5 and injects the fuel in the direction of the transfer passage way, as diagrammatically shown in FIG. 1.

In FIG. 2 there have been shown all the parameters involved in the construction of an engine according to this invention.

In this engine, the smallest diameter of the opening of the transfer passageway 6 into the prechamber 5 is at most equal to 0.6 D D being the diameter of the cylinder bore expressed in millimeters.

The smallest diameter of the transfer passageway hereabove referred to is the minimum diameter d of the passageway, the latter having also an enlarged section 6b at its opening into the prechamber.

In addition, the annular clearance between the protrusion 8 and the wall of passageway 6, when the piston is at the top dead center position, has a valuej at most equal to 0.05 D" D being still the cylinder bore diameter expressed in millimeters.

Finally, the height of the protrusion is so determined that, when the piston moves apart from the top dead center position, the passage section left free for the gases between said protrusion and the wall of the transfer passageway becomes equal to the minimum opening section s (FIG. 1) of the transfer passageway into the precombustion chamber, when the crankshaft has rotated from the piston top dead center position through an angle expressed in degrees of crankshaft rotation corresponding to between one half the duration of injection at full load and the whole of said duration.

The minimum opening section of said passageway is indicated by reference s on FIG. 1. It is the minimum inlet section for the gases into said prechamber, and not the section of the enlarged portion 6b of the passageway 6.

FIGS. 2A to 2C illustrate three positions of the protrusion 8 as it moves downwardly out of the passageway. As is clearly shown in FIGS. 2A and 2B, the passage offered to the gases (dashed arrows) issuing from the prechamber between the boss 8 and the lower edge of the transfer channel 6 does not become equal to the minimum section s of the transfer passageway until after the boss 8 has moved to a position spaced further below this lower edge such as shown in FIG. 2C. Condition c discussed above corresponds to the control of the injection duration such that the boss 8 is in the position shown in FIG. 2C when the crankshaft has rotated from the piston top dead center position through an angle corresponding to between one half the duration of injection at full load and the whole of said duration.

It will be understood that the present invention is related to engines having conventional injection timing with start of injection preceding top dead center position by a generally similar crankshaft angle for both small and full load operation with end of injection for full load following the top dead center position by a greater amount for full load than for partial load. For example, injection at small load from approximately 10 preceding the top dead center position to approximately 10 following the top dead center position and injection at full load extending to approximately 20 following the top dead center position could be utilized with the present invention. It will also be understood that conventional ignition initiation shortly prior to the top dead center position, such as 2 to 3 prior to the top dead center position could be utilized.

In the diagram of FIG. 3 the abscissae are the piston displacements from the top dead center position, expressed in degrees of crankshaft rotation and the ordinates are the percents of burned fuel during the progress of the combustion. In this diagram the curves 10, 11 and 12 respectively relate to three different types of engines.

The first type of engine, to which corresponds the curve 10, is a direct injection engine of conventional type wherein the maximum pressure in the combustion chamber is 140 atmospheres, the mean effective pressure being 16 atmospheres.

The curve 1] relates to an ideal engine wherein the combustion would progress at constant pressure.

Curve 12 relates to an engine according to the invention, running with the same mean effective pressure of 16 atmospheres as the conventional engine corresponding to curve 10, said engine having the same cylinder bore and consequently the same power output as the conventional engine, but running with a maximum pressure in the combustion chamber which is not higher than atmospheres.

This engine when running with a maximum pressure of atmospheres can produce a mean effective pressure of 26 atmospheres resulting at equal cylinder bore in a power increase of about 60 percent with respect to a conventional engine running at a maximal pressure of I40 atmospheres in the combustion chamber.

This remarkable improvement in the engine performance can be more easily understood when comparing (FIG. 3) the curve representative of the progress of the combustion in an engine according to the invention(- curve 12) to the ideal curve representing the progress of the combustion at constant pressure (curve 11) as it is apparent from said comparison that curve 12 is very close to curve 11.

As compared to engines commonly used, having substantially similar characteristics the engine according to the invention further exhibits the very considerable advantage of discharging to the atmosphere exhaust gases containing only a reduced proportion of polluting substances.

Comparative measurements have been carried out with an engine of the direct injection type an engine with a precombustion chamber of the conventional type and an engine with a precombustion chamber as modified according to the characteristic features of the invention said three engines having substantially equal mechanical performances.

The engine according. to the invention was a supercharged Diesel engine having six cylinders with a cylinder bore diameter of 185 mm and a nominal power of 900 HP at a running speed of 1,500 rpm.

The measurements carried out at the testing bench on engines running at full charge, relate to the fumes and nitrogen oxides contents of the exhaust gases.

1. Exhaust Fumes A determined volume of exhaust gases from each engine is taken and passed through a filter of determined surface and porosity. The soots contained in the exhaust gases thus darken the filter surface which is compared by any known means to a conventional standard darkness scale called Bacharach scale.

There is thus determined a fume index which is the higher as the fume content is greater.

The results of the measurements are as follows:

direct injection engine index 8.5

engine with precombustion chamber of conventional type:index 7 engine according to the invention index 4.5 2. Nitrogen Oxides The measurements carried out in the same conditions gave the following results:

direct injection engines: nitrogen oxides content of 1,400 ppm (parts per million of parts) engine according to the invention: nitrogen oxides content of 700 ppm.

These results make clearly apparent the further advantages of the engines according to the invention in the field of the action against atmosphere pollution by the exhaust gases discharged by the compressionignition engines.

What we claim as this invention is:

1. A compression-ignition engine having at least one cylinder, the bottom of which cylinder is provided with a prechamber communicating with the cylinder through a transfer passageway, a piston provided with a protrusion adapted to penetrate said transfer passageway towards the end of the compression stroke, and a fuel injector opening into said prechamber for injecting fuel in the direction of the transfer passageway, wherein the combustion proceeds at substantially constant pressure as a result of the combined use of the following characteristic features:

a. the transfer passageway opens into the prechamber through an opening whose smallest diameter expressed in millimeters is at most equal to 0.6 D, D being the diameter, expressed in millimeters, of the cylinder bore, and

b. the annular clearance between the protrusion and the wall of the transfer passageway, when the piston is at the top dead center position, is at most 0.05 D, D being also expressed in millimeters.

2. An engine according to claim 1, further comprising the characteristic feature:

0. the height of the protrusion is so determined that, during the downward stroke of the piston, the flow section left free for the flow of gases between the protrusion and the lower edge of the transfer, passageway becomes equal to the minimum section with which the transfer passageway opens into the precombustion chamber, when the crankshaft has rotated from the piston top dead center position through an angle expressed in degrees of crankshaft rotation corresponding to between one half the duration of injection at full load and the whole of said duration.

3. An engine according to claim 1, wherein said protrusion is substantially cylindrical with a constant diameter along its length.

4. An engine according to claim 2, wherein said protrusion is substantially cylindrical with a constant diameter along its length. 

1. A compression-ignition engine having at least one cylinder, the bottom of which cylinder is provided with a prechamber communicating with the cylinder through a transfer passageway, a piston provided with a protrusion adapted to penetrate said transfer passageway towards the end of the compression stroke, and a fuel injector opening into said prechamber for injecting fuel in the direction of the transfer passageway, wherein the combustion proceeds at substantially constant pressure as a result of the combined use of the following characteristic features: a. the transfer passageway opens into the prechamber through an opening whose smallest diameter expressed in millimeters is at most equal to 0.6 D3/4, D being the diameter, expressed in millimeters, of the cylinder bore, and b. the annular clearance between the protrusion and the wall of the transfer passageway, when the piston is at the top dead center position, is at most 0.05 D3/4, D being also expressed in millimeters.
 2. An engine according to claim 1, further comprising the characteristic feature: c. the height of the protrusion is so determined that, during the downward stroke of the piston, the flow section left free for the flow of gases between the protrusion and the lower edge of the transfer, passageway becomes equal to the minimum section with which the transfer passageway opens into the precombustion chamber, when the crankshaft has rotated from the piston top dead center position through an angle expressed in degrees of crankshaft rotation corresponding to between one half the duration of injection at full load and the whole of said duration.
 3. An engine according to claim 1, wherein said protrusion is substantially cylindrical with a constant diameter along its length.
 4. An engine according to claim 2, wherein said protrusion is substantially cylindrical with a constant diameter along its length. 